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In a media appearance a few days before the Dec. 12 special election in Alabama, U.S. Sen. Susan Collins, a Republican from Maine, indicated that her colleagues would have to seat controversial Alabama Republican Roy Moore in the U.S. Senate if he wins. “If he is elected, there are no grounds under the Constitution to fail to seat him,” Collins said. Is she right?

Collins is correct based on a U.S. Supreme Court decision nearly a half century ago. But the Constitution does permit the Senate (as well as the House) to censure and expel members, even shortly after they take a seat. That seldom happens, however, and hasn’t occurred in the Senate since the Civil War.

The relevant Supreme Court decision stems from the House of Representatives’ refusal in 1967 to seat Democratic Rep. Adam Clayton Powell Jr. of New York, who had been charged with misappropriating public funds, among other allegations. Powell’s lawyers sued, arguing that the House had to seat the political icon from Harlem because he met the “standing qualifications” set out in the U.S. Constitution — age (25 for the House, 30 for the Senate); citizenship (at least seven years for the House, nine years for the Senate); and inhabitancy in the state he was elected to represent.

Powell’s case reached the U.S. Supreme Court in 1969. In Powell v. McCormack, the U.S. Supreme Court held in an 8-1 decision that Congress is limited to the standing qualifications expressly prescribed by the Constitution in judging the qualifications of its members. The decision came after Powell had run – and won again – in a special election to fill the seat he had initially been denied. And it affirmed that the House had no choice but to seat Powell.

“[C]ases may readily be postulated where the action of a House in excluding or expelling a Member may directly impinge upon rights under other provisions of the Constitution,” Justice William Douglas said in a concurring opinion. “…Suppose, for example, that a Member was excluded or expelled because of his religion or race, contrary to the equal protection clause, or for making an unpopular speech protected by the First Amendment. … [E]xclusion of the Member-elect on grounds other than age, citizenship or inhabitancy could raise an equally serious constitutional issue.”

But the Supreme Court has not addressed whether expulsion of a member of the Senate, once seated, is subject to court review. The official history of the U.S. Senate shows that since 1789, the Senate has expelled only 15 members, and 14 of those were charged with support of the Confederacy during the Civil War. In several other cases, the Senate considered expulsion proceedings, primarily because of alleged corruption, but either found the member not guilty or failed to act before the senator resigned.

The Constitution requires two-thirds vote to expel a member. Therefore, a successful motion to expel Moore, if he wins, would require significant Republican support in the 52-48 majority Republican Senate.

“If the voters of the state, fully knowing all of these allegations, nevertheless choose to elect Roy Moore, is it appropriate for the Senate to expel him?” Collins asked at a recent media breakfast. “I think that’s a really difficult question, and I don’t know the answer to that yet.”